The proposal is for a continuation of our work on laryngeal receptors and an extension of this work to other regions of the upper airway (pharynx, nose) for which there is a substantial lack of knowledge in terms of afferent innervation. An experimental protocol (Aim #1) will study the properties of laryngeal receptors responding to irritant of physical and chemical nature known to cause cough and/or bronchoconstriction. Another protocol (Aim #2) will verify the possibility of changing the response of laryngeal cold receptors by changing the local perfusion. Local inflammatory processes could alter receptor function and thus the corresponding reflexes. The same protocol will be used to ascertain the specificity of menthol as a stimulant of laryngeal cold receptors. If effective this substance could be used as a tool to study the reflex effects of these endings. The experimental protocols designed for the study of pharyngeal (Aim #3) and nasal (Aim #4) receptors are based on our previous work on the larynx and will ascertain the presence in these areas of the upper airway of pressure, temperature and muscle contraction sensing endings. This fferent information is likely to play a significant role in the mechanisms preserving airway patency. The last project (Aim #5) concerns the role of the cricothyroid muscle in modifying upper airway resistance. The use of reversible paralysis of this and other laryngeal muscles, while the animal breathes spontaneously, should provide new and reliable evidence. Is the activity of this muscle useful or detrimental in cases of recurrent laryngeal nerve paralysis?